Let's look at it this way. Here are all the options (as I can figure based upon the info you provided)
Leased Line: Leased lines can be had at various speeds from telcos. A T1 is a leased line. So is a T3, OC12, etc. The pros of a leased line is that it is
dedicated bandwidth. The contract will normally lay our a service level agreement that dictates a minimum bandwidth and uptime as well as how fast the service will be repaired in the event of a problem. The cons of a leased line are that they are expensive and require equipment installed on both ends. This means that your friend will need to work with NYSE to connect to their network. How feasible that is depends upon his relationship with them and what is going on.
Cable: As mentioned by j-dogg, cable is a shared medium. It also would require that your friend goes over the Internet and connect to NYSE via a VPN of some sort. Both of those, combined with the shared part, make bandwidth a flexible thing. There are no guarantees. Even if the local cable company has a business service with SLAs and such, once you hit the 'net all bets are off.
FIOS: FIOS (which I have) is great. The speeds are excellent (in both directions) and Verizon is now offering a 20/20 service with 20mb up and down. And from a cost perspective it does not cost much more than Cable. The drawback is that you would have to go over the Internet and VPN, which means bandwidth guarantees are not possible.
So a
leased line would be the best bet, but requires the cooperation of NYSE to setup the dedicated connection. Knowing the business NYSE is in, I would guess that this kind of setup is not something that is new to them and they have a procedure for allowing someone to connect a leased line to their network. As for what speed line to get, that all depends on how much data he wants to move and how fast it needs to be done. Here is some speed information, all speeds are symetrical (same up and down):
Traditional Leased Lines
T1 = 1.544 Mbps
T3 = 44.736 Mbps
OC Lines (SONNET, Fiber)
OC-1 = 51.84 Mbps
OC-3 = 155.52 Mbps
OC-12 = 622.08 Mbps
OC-48 = 2488 Mbps (yes, that is 2.5Gbps)
And it goes up from there to
OC-768 (39.6 Gbps).