Whether its worth the extra money or not depends on how far away you are from it.
it seems that Infinity 2 rapidly loses performance over certain distances.
The chart below was supplied by Thinkbroad,it is for Digital Region,whether its the same for other fibre connections I'm not sure but it will give you a rough idea.
I'm not sure that table is very helpful, seeing as what you need to know is line length to cabinet rather than line-of-sight distance to cabinet, which it appears that chart is based on.
There are plenty of reports of people being very close to the cabinet but the actual line goes round their estate before going back to the cabinet, making them actually quite far away in line length.
I myself am around 110M from the cabinet with my line length approximately 230M to the cabinet (based on tracing my lines real path on Google Earth).
My max attainable speed is ALWAYS over 110Mbit (thank you HG612). However, Digital Region in their infinite wisdom have me capped at 70Mbit, in fact they currently cap ALL residential customers at 70Mbit max.
So it makes that table all the more questionable as how can they know how close you need to be to get 100Mbit if nobody on the network is being allowed to sync at that speed?
If its based on speed test results then that is even less accurate, as the TBB speed test NEVER achieves my maximum data rate, speedtest.net does however.