Regarding my reference to "agility:"

I hear words to this effect every now and then.

Given the OP's weight of 140 lbs, I guessed a frame size of 56 cm and I assigned a tire size of 32 mm.

Plugging the geometry of the respective frames, with 32 mm tires, into the various trail and flop calculators I use, I found that the Cross Check has a trail of 61 mm and a flop of 18 mm; and, in comparison, the Surly Steamroller has a trail of 57 mm and a flop of 16 mm.

For those not familiar with trail and flop, the bicycle industry considers a trail range from 50 mm to 70 mm the norm, with 50 mm as quick and 70 mm as slow.

I have three fixed gear bikes that range from 59 mm to 67 mm in trail, and they all feel good.

The so-called quick bikes handle much better at lower speeds, and the so-slow bike does OK at lower speeds but handles unexpected wheel-deflecting bumps better than the quicker bikes; meaning, I don't feel as much handlebar twist when I hit something with the "slow" bike.

Given that I ride mostly in the 15 mph range, the quicker bikes feel "just right" to me, but I wouldn't want to ride them on a downhill at 35 mph.

For those who want to know, flop refers to the tendency of a turning bike to "fall" into the turn, remain neutral, or "climb" in the turn.

In the case of the Cross Check and the Surly Steamroller, not enough differences exist in the trail and flop numbers to matter, except to the extent that both bikes look like they will handle better at lower speeds than at higher speeds.

Agility doesn't mean "twitchiness," nor "squirreliness," but, rather, means agility.

If you live in the 15 mph range, agility pays off as long as it doesn't include instability.

Instability, in this usage, means the tendency for a divergence to increase, as one might see with a high flop number (once it starts to turn, it wants to turn more, and especially at low speeds).

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I think too much gear on the body represents a bad thing.

I also find a low mass bike more pleasant to ride.

I think I would experiment with distribution, with water bottles on the frame, solid items on the saddle rack, and soft items on my body.

By the way, I love the picture of the Steamroller posted by gmacmt.

Yes, but the misery happens at a certain high speed that I don't see that often on my fixed gear bikes.

Granted, sometimes I think about putting a front fender back on my weather bike, but not often enough to do it.

How much rain does gmacmt expect to see at the time of his ride?

We have a very wet early spring here in the Northwest, and then it dries up starting in May.

That makes sense, and seems obvious now that you've shared it.

The various patagonia micropuff synthetic down jackets I could find on line looked very suitable for your use.

Thanks for sharing all of this good information.