</font><font color="blue" class="small">( My tractor calls for 2600 rpm to achieve 540 pto output. My question is that with my finishing mower it cuts just fine at 1800 to 2000 rpm, will this damage the gear box on the finishing mower? Just how important is 540 Pto on most attachments? Such as rotary mower, sickle mower etc? [/list] )</font>
I think it's the safe maximum RPM.
For rotary cutting, I get great benefits for running at lower RPM than 540 when cutting light weeds and grass. The best benefit is the edge on the blade lasts much longer with a mere 100 RPM reduction. That way, you can run a sharper blade and really CUT instead of "bruise" the grass. Lower blade RPM also prevents much power and fuel robbing re-cutting of the grass and attendant "fluff balls" that stand up high and do not rot quickly. Lower RPM also reduce noise and reduce wear on the tractor and cutter drive line.
I also run my 6 footer at 1800-1900 rpm, which is somewhere around 450 PTO RPM I guess. I inspect my blades every time I cut, and keep them really sharp. Lately I need to do a 5 minute touch-up on them every time or 2 I mow.