I belive you are correct... charging at 6 amps will likely give slightly higher discharge numbers then if you chared at 5 amps. However, it's a very small differance from what I hear, and for the most part doesn't make any significant differance.
Keep in mind too that even amongst the same matchers equpment, there will be small differances in the numbers as a result in diffferances between one 4 cell matcher and another. These differances are likely to be greater then the differance you'd see between a cell charged at 5 volts, vs 6 volts...
IMHO one of the most important asspects of any perticular matcher, is how well they maintain their equipment and/or how often and how well they calibrate it.
Measureing differances in 100ths of a volt is very hard to do accuartely on the type of equpment that is in use. Even to get within 5/100ths is likely a difficult thing to do.
It's my further understanding that room temperature where the cells are matched makes noticable differances in the numbers produced...
In other words... Don't get too concerned about a couple hunderths of a volt... Find a matcher you trust, and buy what you can afford.