Hardware concerns for optimal ruby on rails development on ubuntu machine

Question

I've been developing dynamic web sites using ruby on rails on a 5 year old mac mini which has been great except that it takes too much time -- 15 minutes or so -- to run my simple test suites. I believe that I could reduce that time with an upgraded computer running ubuntu. Still, I don't know where the bottlenecks are causing those tests to run slowly. Should I focus on the cpu, ram, hard drive, MOBO and do I even need a video card if my cpu/mobo has some graphics capability?

I've read Build an Awesome PC for 2014 and studied the great component overview at Logical Increments. I put together a preliminary build at PC Partpicker. I was about to post my planed build on Reddit's Build A PC site when I got cold feet. Most of the info I've read is directed towards optimal gaming and I'm not sure how applicable that is for my needs.

I'd be super grateful if anyone had any insights to share regarding what my needs are for optimal ruby on rails web development.

Thanks in advance! Ben

Relevant Current system specs

Graphics/Displays:

NVIDIA GeForce 9400:

  Chipset Model: NVIDIA GeForce 9400
  Type: GPU
  Bus: PCI
  VRAM (Total): 256 MB
  Vendor: NVIDIA (0x10de)
  Device ID: 0x0861
  Revision ID: 0x00b1
  ROM Revision: 3362
  Displays:
    L2270NW:
      Resolution: 1440 x 900 @ 75 Hz
      Pixel Depth: 32-Bit Color (ARGB8888)
      Display Serial Number: 0
      Main Display: Yes
      Mirror: Off
      Online: Yes
      Rotation: Supported
    L1916HW:
      Resolution: 1280 x 800 @ 60 Hz
      Pixel Depth: 32-Bit Color (ARGB8888)
      Display Serial Number: 0
      Mirror: Off
      Online: Yes
      Rotation: Supported
      Adapter Type: Apple Mini DisplayPort To VGA Adapter
      Adapter Firmware Version: 1.03

Hardware:

Hardware Overview:

  Model Name: Mac mini
  Model Identifier: Macmini3,1
  Processor Name: Intel Core 2 Duo
  Processor Speed: 2 GHz
  Number of Processors: 1
  Total Number of Cores: 2
  L2 Cache: 3 MB
  Memory: 8 GB
  Bus Speed: 1.07 GHz
  Boot ROM Version: MM31.0081.B06
  SMC Version (system): 1.35f0
  Serial Number (system): YM90634W19X
  Hardware UUID: B368DCBF-F005-5126-BF7C-BC2ED886642E

Memory:

Memory Slots:

  ECC: Disabled

    BANK 0/DIMM0:

      Size: 4 GB
      Type: DDR3
      Speed: 1067 MHz
      Status: OK
      Manufacturer: 0x857F
      Part Number: 0x483634353155363446373036364700000000
      Serial Number: 0x00000000

    BANK 1/DIMM0:

      Size: 4 GB
      Type: DDR3
      Speed: 1067 MHz
      Status: OK
      Manufacturer: 0x857F
      Part Number: 0x483634353155363446373036364700000000
      Serial Number: 0x00000000

Serial-ATA:

NVidia MCP79 AHCI:

  Vendor: NVidia
  Product: MCP79 AHCI
  Link Speed: 3 Gigabit
  Negotiated Link Speed: 3 Gigabit
  Description: AHCI Version 1.20 Supported

    OWC Mercury Electra 3G SSD:

      Capacity: 120.03 GB (120,034,123,776 bytes)
      Model: OWC Mercury Electra 3G SSD            
      Revision: 501ABBF0
      Serial Number: EX3G12012E08H9170   
      Native Command Queuing: Yes
      Queue Depth: 32
      Removable Media: No
      Detachable Drive: No
      BSD Name: disk0
      Medium Type: Solid State
      TRIM Support: No
      Bay Name: Lower
      Partition Map Type: GPT (GUID Partition Table)
      S.M.A.R.T. status: Verified
      Volumes:
        disk0s1:
          Capacity: 209.7 MB (209,715,200 bytes)
          BSD Name: disk0s1
          Content: EFI
        Macintosh HD:
          Capacity: 107.1 GB (107,101,011,968 bytes)
          Available: 8.86 GB (8,863,625,216 bytes)
          Writable: Yes
          File System: Journaled HFS+
          BSD Name: disk0s2
          Mount Point: /
          Content: Apple_HFS
        Recovery HD:
          Capacity: 650 MB (650,006,528 bytes)
          BSD Name: disk0s3
          Content: Apple_Boot
        Untitled 2:
          Capacity: 11.94 GB (11,939,131,392 bytes)
          Available: 235.2 MB (235,216,896 bytes)
          Writable: Yes
          File System: Journaled HFS+
          BSD Name: disk0s4
          Mount Point: /Volumes/Untitled 2
          Content: Apple_HFS

NVidia MCP79 AHCI:

  Vendor: NVidia
  Product: MCP79 AHCI
  Link Speed: 3 Gigabit
  Negotiated Link Speed: 1.5 Gigabit
  Description: AHCI Version 1.20 Supported

    PIONEER DVD-RW  DVRTS08:

      Model: PIONEER DVD-RW  DVRTS08                 
      Revision: Q81B    
      Native Command Queuing: No
      Detachable Drive: No
      Power Off: No
      Async Notification: Yes
      Bay Name: Upper

Software:

System Software Overview:

  System Version: Mac OS X 10.7.5 (11G63b)
  Kernel Version: Darwin 11.4.2
  Boot Volume: Macintosh HD
  Boot Mode: Normal
  Computer Name: XXX’s Mac mini
  User Name: xxx (xxx)
  Secure Virtual Memory: Enabled
  64-bit Kernel and Extensions: Yes
  Time since boot: 15:31