I had the same sort of dilemma when looking at copies of Windows 7. I only saw a few messages on the Internet from people saying they had problems with a branded (like HP, Dell etc.) copy of Windows. But, I decided at the last minute, instead of buying Windows half price, I bought the Windows 7 (64-bit) OEM Professional at newegg.ca (well, .ca because I'm in Canada).
I really like the Aero Glass desktop theme on Windows 7 and intend to keep this machine as a secondary machine when Windows 10 comes out.
Sort of off-topic but if you really want to know what I think of doing a build right now... When I tried Camtasia 7 for a 2 and a half hour recording, an old machine with an Intel E8500 took over 6 hours, my current Intel i5-4570 with 8GB of RAM took 2 hours 45 minutes. So, right before the 2016 Olympics, I might be looking at getting an Intel Skylake CPU, 4K (or actually UHD) monitor and 4K (UHD) Blu-ray drive. I'm hoping it will only take 1 hour and 30 minutes for a 2:30 recording. We'll see I guess. 🙂