Latest edition of the Journal of Strength and Conditioning JASC Sept 2010 (Vol 18, Issue 3)has a submission on 'Comparing the speed and strength-related physical qualities of NRL and QLD Cup Rugby League Players (wingers and centers)'
The sample size of the testing is so small (20 subjects in total) that conclusions are few, however here are some of the findings that may be of some interest and it must be pointed out that the data was collected by the researchers via correspondence with the coaches at the clubs; there was no single tester for the data collection.
AVG BW, 3 rep max Squat, 3 rep max Bench, Vert Jump, 40m dash
NRL Centers 96kg, 165kg, 139kg, 71cm, 5.03
QLD Cup Centers 89kg, 151kg, 120kg, 60cm, 5.55
NRL Wingers 90kg, 157kg, 129kg, 72 cm, 4.84
QLD Cup Wingers 86kg, 155kg, 129kg, 69cm, 5.04
A lot could be said about the paper and the data. A few comments I would make would be on what I consider very poor squat and vertical jump numbers. The nature of the test itself would need some further investigation (we all know about squat numbers; vertical jump I have seen assessed a few different ways) but the squat numbers were called 'full depth' squats and if that is the case those are poor results for professional football players in my opinion and even worse if they are the sort of quarter squats that are regularly performed. The vertical jump numbers to me reflect the poor lower body strength.
The results are consistent with what I have observed directly and by personal correspondence with Rugby League athlete development; the data here is of course a very small sampling as I stated, but I'm not surprised by it.