As I understand it (and hopefully i am not completely wrong..) you don't have to 'store' a list and 'then' read again it to find the max magnitude. It's as simple as the following:

(some signal) *I* *I* [pd metro@samplerate] *I*/ [vsnapshot~ ] | [abs ] | [moses ]X[t f ]            |         [f ]

I think I may have misunderstood your task earlier. In any case, you'll probably still do what you want more efficiently at the signal level:

[inlet~] [block~ 1] | [abs~] [delread~ $0-compare 0] | / | / [max~] |
|
| [delwrite~ $0-compare 1] | [outlet~]

The [delread~] should be a one-sample delay, so you're just comparing the previous maximum with the current sample and outputting the larger of the two. Then on the outside you can poll that with snapshot~ periodically just like you did your float object above. If you need to reset it, I think you can just have the [delread~] feed into a [*~] with a [line~] that jumps from 1 to 0 and back to 1. Use [switch~ 1] instead of [block~ 1] if you want to be able to test the cpu load from that patch. I hope this works.

I don't think that [env~] does what you want it to at all.

Matt