As others have mentioned already the simple answer is, "it depends."
54G = 22-24Mbps
150N = 40-60Mbps*
300N = 70-90Mbps*
300N = 110-130Mbps**
450N = 150-200Mbps**
* = Cleaner the signal the higher you can get but it will max out around there.
** = 5Ghz range with a 2x3 or 3x3 wireless card in your laptop (3 antennas).
So for 75Mbps i'd say get a dual-band device such as the Netgear WNDR3700, 3800, 4000, 4500 or the Linksys E4200, EA2700, 3200 or 4500.[rant]
You never mentioned the wireless router/access point your using.
At that speed you can max out a lot of wireless devices on the throughput. However just because you have a 75Mbps connection doesn't mean your always going to get that speed from the server(s) your connecting to. So the internet is the bottleneck at times....
I always see people say this and it irks me to death
. I'm not getting a 300Mbps connection to load "neowin.net" faster, i'm getting it so that when i'm downloading from a few 6-12GB files from "Microsoft.com" my connection doesn't stall out when i'm trying to stream netflix also as well as other people playing Xbox in the house. Remember the days of 56K where you basically did 1 thing at a time? You were either downloading or browsing, you hate doing both at the sametime because at 4KB/s your 56K line woud be saturated and browsing would just be painful!
Not attacking you by the way, that's just 1 thing I see people always mention when it comes to a connection faster than 10Mbps or something on tons of different sites. The first statement is that it must be something illegal!
Ok back on topic now, sorry for the little rant