I'm not a speedball player so can't comment too much on the specifics for that, but in general there are two types of padding in paintball.
There is the protection for crawling etc, but in addition there is the bounce effect.
With relation to the players position they are marketing different pads for players who may have different needs - I assume that a back player is further back and does not crawl as much, a front player needs to be agile and mobile, but could be diving onto their arms, crawling a lot and quickly and with more chance of being shot up close so can hope for a bit of extra softness for bounce / impact absorbtion.
Depending on how you play you may or may not need different forms of protection.
However make sure you do protect your elbows. A couple of years back I took up elbow protection properly for a very good reason - I grew one of these:
http://en.wikipedia.org/wiki/Olecranon_bursitis