Since you have driven both cars and I did not have a chance with the E60 M5 I refrain from arguing against you. However, your strong belief
made me curious and I checked the data for M5. I thought some respectful tests done at the time would be more fair to judge the E60 M5 cause there are comparisons nowadays underlining how much better or faster the F10 is (by the way I personally couldn't like the new M5 much, I would take the E60) and I found that Autocar (I respect their detailed road tests) has some good data for the M5 from 2004 as well as their 2011 road test and data for the 1M. You can find both in internet easily and maybe u r already familiar with them so I am not attaching anything here. The relevant data is printed and sitting in front of me right now:
The acceleration: Till 60mph 1M is faster and they get even at 4.6s. at 60mph. After that slowly the M5 pulls away and the distance at 150mph is simply huge: the 1M reaches there at 31.3 sec. while M5 needs only 21 sec. Impressive stuff. Standing quarter mile 12.8 s. at 119 miles for M5 and 13.3 s. at 109 miles for the 1M.
In gear times: 1M better almost everywhere.
Brakes: 1M has better numbers.
There is more performance data about the 1M than the M5 and I think it is kind of natural that the 1M would post better times on almost any track which we already knew from the press but I conclude that probably you were more right than I was and an acceleration race between the two with pro drivers in both should finish in favour of the E60 M5 IF we are talking about a race continuing after the 60mph threshold on a long straight. In terms of performance that seems to be the only area that the E60 M5 has a clear upper hand over the 1M.