Very loaded question. Only way to respond is an answer with a mouthful of qualifiers.
From a throughput perspective, 802.11n in a radio and antenna configuration on both AP and client that is capable of 300,000,000 bits/second PHY interface data rate (n can actually go as high as 600 Mb/s as defined in the spec) -- herein referred to as 300 Mb/s (network interfaces are rated in base 10, decimal using standard K, M, G prefixes unlike file sizes and memory which use base 2, using Ki, Mi, and Gi prefixes) in a green field with single client with line of sight at fifty feet without interference will be able to achieve 30 Mb/s at both the PHY and at the application layer with UDP L4 transport or TCP L4 transport with a modern OS tuned TCP implementation and traditional LAN latency of less than 5ms. Application layer throughput of 30 Mb/s puts PHY throughput > 30 Mb/s. Maximum sustained throughput will likely be higher, but 30 Mb/s sustained is very feasible given the qualifiers.
Reduce RSSI or introduce spectrum interference which ultimately introduces latency which ultimately throttles down TCP and whatever your green field maximum is for a given system begins to drop.
With that said I use Cisco 1242AG access points (a/b/g capable, not n) in both a and g paradigms and am able to sustain between 20 - 25 Mb/s application layer throughput (SMB, CIFS, FTP) on the local LAN (out of 54 Mb/s possible at the radio PHY) with a single client at about fifty feet through a single interior wall. However, spectrum interference does cause noticeable drops in throughput.
Moving from a/g to n will only increase the maximum throughput and reliability. However, it is wireless -- and until you test it -- all bets are off.