Yeah I've found the signature checks to be fairly intensive on the game, without them people log into the lobby instantly however with signature checks on there is a delay that can sometimes be 10 seconds or longer before anyone can click from within the lobby and a lot of people do time out during the check.
As for disk activity we run multiple SSD drives in Raid 0 and disk read/write access times are under 1ms with wait times of 0 and read/write performance isn't an issue, in fact the least capable node we run is a xeon 1230v2 with 32gb ram, 2x 256GB samsung 830 SSD drives in raid 0 (LSI 2960-4i BBU 512meg cache) this also has dual 1Gbit ethernet connections, providers are a mixture however level3 is the primary provider so you can't get much better than that.
Even though the game can't use the resources allocated to it on on our least capable hardware node, we have tested it on higher performance hardware with different disks/raid card combinations, CPUs etc it makes no difference as expected yet benchmarks on all of the items listed turn out as expected.
Doesn't really matter what you connect with (my PC is fairly high spec) there are fairly large delays with sig check 2 enabled, we've tested this on multiple different hardware configurations which all involved SSD drives and it was the same result, so performance improvements here would be fantastic.