The generic answer is "it depends" - on your equipment, location, provider and needs.
That said, based on your description (and assuming it is, indeed representative), you will probably not notice the difference between 150 mbps and 250mbps - for the following reasons -
- Your current performance is less then 150 megabits. Assuming that this is not due to your ISP deliberately placing caps on your performance (or at least assuming they won't cap the 150 megabit connection more then the 250 megabit connection) you will not see a performance decrease. (Its quite probable that your equipment is the bottleneck). IN EFFECT, ANYTHING YOU ARE PAYING FOR OVER 90 MEGABIT IS MONEY DOWN THE TOILET - YOU ARE NOT USING WHAT YOU ARE PAYING FOR.
Things to note -
The only things which use a considerable amount of bandwidth from your list are the Roku devices. Without having access to one, I expect these would use way less then 10 megabits of Internet bandwidth each. (1.5 - 4 mbps would be typical for a high definition stream).
Games would come next in terms of bandwidth utilisation - generally though, these require low latency, not lots of bandwidth. The difference in latency between a 150 megabit and 250 megabit would not be perceivable. (Less then 1 ms)
WIFI devices are generally not capable of transmitting/receiving more then about 75 megabits, and typically not even this much. Your Tablets don't have the processing power to sustain anything close to this, and IOT device bandwidth usage is trivial.
The scenarios where 250 megabit WOULD make a difference -
1. Lots and lots of users (way more then a typical family)
2. Editing and working with uncompressed Video and sending/receiving the same - think of commercial movie production. (Streaming is highly compressed)
3. Family members who are addicted to torrenting - and don't know how to limit the speed of their connections.
4. Providing (serious) web server or similar hosting.
To put this in perspective, 150 megabits equates to 48600 gigabytes of data per month (in each direction). That is 2 orders of magnitude more then your typical heavy Internet user will use. (Compared to 81000 gigbytes on 250 megabit plan). Your heaviest use - A typical high def video would be in the order of 1 gig of video per hour - so if you were streaming high def video 24/7 you would use about 720 gigs of data per month - x 2 for 2 devices = 1400 gigs of data, which is still < 3% of your capacity.
Lower speed than in your contract may have several reasons: your network devices can't provide full speed, other devices use bandwidth, ISP provides less than in the contract... Before investigating the reason it's not possible to tell you what would be the reason of decreased speed. – Máté Juhász – 2018-06-30T18:35:14.263
2You are using Wireless on your laptop that you perform the speedtest on, aren't you? Your wifi is slower than the ISP speed, and because of that, you are not getting the speed. Download speed is not the only factor though. Upload speed matters just as much. It is possible the upload speed of the slower connection will become a bottleneck, and if that's the case, everything will slow down to a crawl. First, hook your laptop up with a wire, and perform the speedtest again. It is likely now 250 mbit. – LPChip – 2018-06-30T18:45:17.607