First - Cat 6 is a waste of money - Cat5e is all you need for gigabit. I run about half a mile of it (all in less than 100m chunks, of course) on switches that report error rates, and see no point whatever to buying Cat 6 - it won't really run 10G-baseT, and if it won't to that, there is no point to it - and little enough point to something that will.
Wirewise, you'll generally find that in real life, 100Mbit wire will beat wireless unless you are sitting in the same room as the router and a patch-cord would be all the wiring you'd need to do there. Gigabit blows wireless out of the water. However, gigabit also tends to exceed other components of the chain - some cheap gigabit adapters will make the gigabit link light light up, but can't actually move data that fast. Given that the router you have purports to have gigabit ports, it's intertesting that you get much slower wired connections through it than with a crossover cable, so it may be of that class. It's certainly "home-consumer-grade" equipment. Disk subsystems may not really have the throughput to keep up, etc. Gigabit just moves the squeeze point to somewhere other than the network speed, but that's a good thing, generally.
Wirelessly, again, unless you have short clear line of sight, 2.4 Ghz may well move data a lot faster than 5 Ghz - it penetrates building materials better, so you get more signal, so you get a better connection, so data moves faster. Assuming you have dual-band, try it. I was utterly unimpressed with my shiny new 5 Ghz wireless AP when I got the first one and saw 5Mbit connections on 5 ghz and 20Mbit on 2.4 for the same client computers. Unless 2.4 is so polluted your local router is overwhelmed by other signals around you, 2.4 beats 5 in most cases. You don't have to have empty air, you simply need to be the AP closest to your equipment with the best signal, and 2.4 can often do that in your own space better than 5 GHz can.
IMHO, spend the money once and wire the place, and get a real switch since the netgear slows you down on wires.
As for real-life, limited by whatever, speeds on wire, I can't say for your particular hardware and software, but my Mac, connected by gigbit to a 3 com gigabit switch, connected by gigabit to a Mac server, pulls somewhere around 360Mbit (45MByte), so I'd guess you could see the 40MByte you saw with a crossover cable if you were paying attention to b .vs. B when you wrote that part. When connected to a USB2 disk, rather than the internal disk, that drops to 67Mbit or so, as the USB is the bottleneck there.
Add: You might also try whichever computer gets the best signal on 5Ghz on 5, and the others on 2.4 - that will reduce contention for airtime (among your computers) if the 5 ghz with best signal is not too much worse than when on 2.4 Ghz.
I would test the speed using a crossover cat5 cable between the server and one of the clients. – drk.com.ar – 2014-04-29T13:22:47.770
Have done that- about 40MB/s average. Router replacement then? – Vincent – 2014-04-29T13:26:29.020
Do those 3 WIFI cards overlap their WIFI channels? If yes, spread them. Note: 5 GHz has other channels
– nixda – 2014-04-29T13:37:44.360I have a 3700(rev2) and I see different speeds. I can get up to 120MB/s to my NAS using Cat5e. Wireless the speed varies between 10-16MB/s for 5ghz and 3-8MB/s with 2.4 ghz (This is a dual band router, no need to decide if 2.4 or 5ghz) – Gotschi – 2014-04-29T15:07:18.420
@nixda - they are connecting to the same access point. So all 4 devices would be on the same channel, logically. – Ecnerwal – 2014-04-29T15:08:09.787
Thanks for all the responses- really appreciate it. I have tried powerline but it only improves transfer rates marginally. All the clients are relatively close to the router ( within 6m radius) hence my use of 5Ghz. Will try 2.4 as suggested. Seems I believed the marketing hype too much when buying the router- 300Mbps/s (approx 30MB/s) on the box led me to believe i would get roughly that. Looks like I'll have to bite the bullet and get some wiring done, as well as getting a proper switch. I am certain the server can keep up with transfers, as it caches most files in ram and on ssd cache. – Vincent – 2014-04-29T15:18:25.827
@Ecnerwal Of course. I misread this – nixda – 2014-04-29T15:24:23.177