Some MOBOs do test memory (not just quick test) during boot up, so it takes some time. Thus, I would say yes; it would affect the boot time. You can disable this testing in BIOS, I believe.
Without the MIMO antenna, you could get up to around 430Mbps. However, that's kinda theoretical speed. I typically expect half to a quarter of those speeds for wireless.
If you're referring the 160gb drive to ST3160811AS, I would like to recommend leaving as is. It's a really silent and small drive, access time isn't that fast. So, I'm only using the seagate drive for back ups.
Although modern wireless mice do not have much lag, stereotypical though that gaming mouse should be wired haunts me all the time. So, I'm always using wired for gaming :).