Thanks for the replies. However, my problem is not leveling as I use Wrye Leveling. This allows me to level when I want (I get 10 attribute points and 15 skill points to distribute as I please) any time I level. There is nor increase in skill or attribute through use so I am in complete control.
Based on the answers, I would probably not want to go above level 25. I do not think there is too much content I would miss by staying at 25 to play the game.
Another aspect that I am looking to change is the weight of potions. Not much challenge at any level if I can carry 50 potions of healing and 50 potions of damage any time I go to clear a dungeon. ROM weighed all potions at 1 so that was nice but can't use that mod in my game. Wry bash has a reweigh potions but I think it only works on potions I have and not ones I make.
Feeling a bit self-sentric, but I'd mention a couple of my less-known mods. http://www.tesnexus.com/downloads/file.php?id=26409 was made to make the game interesting and challenging at higher levels too. The mod completely change the player's health calculation. With this mod, the player's health is a factor of his level, and you set a start health, a health increase per level and a maximum health. By keeping the health increase per level and/or maximum health pretty low, you end up with a player that may be very strong at higher levels, but without the godlike amount of health, making fights still being dangerous. Another use for the mod is that it makes it easier to balance the game since player characters who don't work on their Endurance skills still get the same health.
http://www.tesnexus.com/downloads/file.php?id=25714 is the mod for controlling potion weights. By default it makes all player-made potions weigh 0.2, but you can set the weight to anything you want in the ini. Wry Bash has two reweigh potion options, one for all potions you find/buy, and one for potions you make - but the latter only works for potion types you have already made. As soon as your alchemy level increases or you change alchemy equipment, the potions will be slightly different, and you have to redo WB's reweigh potion function for that savegame, etc. Lightweight Potions works dynamically during your game, so it is just to install and forget.