It's been a while... but I'm sure it hasn't changed...
The speed options via RIVET would normally be 250K or greater; so plan on that, but keep in mind the slower speed (250K) is always a card that could be played.
There are two options for the controllers to get you out of the patterns (mostly not used, but used often enough) via RIVET:
1) giving you a set course time from the hold (TARAL/CULIN/MAKKA) to RIVET or just give a time to cross RIVET if not holding,
2) vectoring you and / or slowing you down and sometime speeding you up depending o what your econ speed is.
By the look of your post I would guess you are talking mostly about option 2. When I was working there I would encourage people to pick a slower speed than they thought they needed then bring you up, rather than doing it the other way around (better for height management); the trade off for that is we could actually cost you a little time and some cranky pilots wouldn't bring the speed back up ie 'you stupid controller you should have picked a better speed'.
I'm a little surprised that you resume before RIVET but can't make the TAMMI requirement, or don't realise you won't make it. I'd guess you'd have at least 40NM to run after being told to resume (ie 20NM before RIVET). Is it because you're not looking for it until after RIVET; is it a design issue with the plate?
Also it's never too late to let us know your not going to make the height requirement, it gives us a chance to point you elsewhere as "the reason for that TAMMI requirement" might just be on your nose or closing on you still. The SY APP controller will not co-ordinate with the Departures controller for arrivals via RVIET/TAMMI, if you bust that requirement you are in DEP airspace and only vigilant controllers may notice before it's too late; the APP guys are worrying more about the CCT and spacing rather than the heights.
So where does that leave us?
Ask if you can have extra miles or higher speed if slowed too much to get back to the profile of A090 x TAMMI (profile, sic); ie go faster for longer = same result.
If getting a clean run, ie not told to hold or slowed early, start down a little early (two mins or so) to give a little vert advantage in your pocket; or set your box to be A090 by 25NM SY and then bring it back up to 20NM (TAMMI) once you hit RIVET, it would be very rare to be slowed after RIVET (excluding the CCT phase) and if you were you could just tell the APP controller directly that you can't meet TAMMI height with a speed reduction then it's very simple for them to give you the options, ie cancel it or work out another plan.
Other than that I'm drawing blanks... But from my ATC view point is the earlier I know the more I can do to help and get you out of the paperwork that follows a bust of the height requirement, there's paperwork for us too; and normally we get in more sh!t than you blokes, such is the nature of that ANSP.