I heartily endorse raising your bars for a long ride. But, do it well before the actual ride so you can get used to the change, and make any other adjustments, possibly to the seat or the levers. I've used a Look Ergo-stem, it's adjustable (got mine off Ebay) so "on the ride" tweeks are possible. Sitting a bit more upright makes the scenery much easier to enjoy, and you tend to look around more which reduces the stress in shoulders and neck. A good trade off for long rides.
Cheers