Synthetic Insulated Pants???

You're probably going to want to try the mediums, as belay pants they're already designed to be worn over layers.
At 6' and 200lbs, the larges were a good fit for me.

Everybody's metabolism is different, but I could never wear synthetic overpants while doing any sustained activity even in sub-zero temps. I usually save them for extended breaks or around camp. If you want to bolster warmth under your softshells you could try polartec power-stretch tights or someting like the R1 bottoms from Patagonia.

I agree, R1 tights and unlined softshells are GREAT for hiking/climbing in -20C weather; for -30 weather I add a set of windproof pants.
I have the micropuffs in a small, I'm the same size as you and take a 30-30. The small fits me well. They are great belay/camp/moving in extreem artic cold and windchill pants.

Thanks guys.

Yeah I hear ya about any movement I stay warm with just long underwear under the champs, I'm looking at putting these on once I stop snowshoeing/skiing for the day and start setting up the tent and cooking dinner and am no longer moving or generating my own heat. Yeah I where 32/30s in jeans so the mediums ought to be roomy enough huh?

No, I wear smalls and they are great – more then enought room to layer overtop my mixmasters and a base layer. I really would go with a small IMO.

They are warm, but not super warm, down pants of the ID ones ARE warmer, the patagonia ones are warm enough though. I like them paired with a DAS parka but FYI they are equal in warmpth to the other micropuff items. In very cold weather you may find that they are not enough in camp. 99% of the time in winter they are great.

I have the polarguard Micropuff pants. I've tried them hanging out in the low teens worn over silk long johns and nylon pants and found them comfortable. I bought an XL because I heard they ran small and that's what was available and find them big on me (6', 200 lbs.). However that makes them easy to put on over whatever I'm wearing and as I'm not going to walk around in them much, I don't find it a big deal. They weigh 16 ounces in XL which is a lot of warmth for the weight. Can't compare them to the ID but I'd imagine the latter are warmer, I just prefer synthetics in my clothing. Oh, price had a definite effect on my decision. ;)

Does anyone know how the Montbell thermawrap pants compare to the Patagonia or ID pants. A little cheaper and lighter. Also are you guys talking about the ID PLQ pants??