It does sound weird for an assassin to carry around a claymore.
Several things you can consider. 1st one is spells. You can either summon something, or you can use variety of spells to aid yourself, like fear, calm, paralyze, push etc and give yourself more opportunities to hit your enemy while on the ground (or run away). You can combine this with weapon enchantment spell, for example adding fire effect to your blade. You can also start using alchemy. Make some poisons, apply them to your weapon, drink a potion that enchances your one-handed damage and hit. Or one that enchances marksman damage and coat your bolt with poison, in your case. You can also use runes.
I play with SkyRe as well, on legendary so things get bad often, so I use all the above. 1st I set up a rune. Then I enchance my dagger with fire damaging spell, coat my blade with weakness to fire spell and equip push in my off hand. I sneak attack the enemy, knock him to the ground with Push, switch to a summoning spell and summon and wack at him. If I see my summon takes too much hits or is running out of time I run back to my rune and summon there, the enemy runs into the rune and then I push him again, resummon and repeat. Another good option that covers pushing and somewhat summoning is the explosive mudcrab one. ![:tongue:](http://www.gamesas.com/images/smilie/tongue.png)
If you have survival mods combined so that you have the wayfarer skill I also suggest using bear traps, either coated with poisons or spells. I put the hell out of those all around the place before I attack someone that's inside of a camp where I know I'll have to fight several enemies.
I also raised fingersmithing to the point where I can steal weapons, so if I have the chance I sneak through the camp and strip them of all the weaponry in the camp and hide it.
Just some ideas. If you don't want any of this I'm afraid your only option is lots of kiting and hit n' run. Or training sneaking up to the point where you can just cut throats or avoid killing overall. If you'll want to kill everyone in every place you'll definitely need more than just your weapon skill and sneaking since enemies simply have too much health and will kill you too fast. If you do decide to use some spells I warmly suggest training speech at least to the point where you can take up silent spell casting, it made my life much easier.
Another spell I forgot about is Illusion's invisibility. That's a really nice option if you decide to use magic, especially if you'd like to come up close to reverse-pickpocket some poisons or steal a weapon but the only way to get to your foe is by a route he's facing towards.
ALSO
if you do decide to use spells and you RP a pro assassin one great combo for killing your enemy and roleplaying that it looks natural and leaves no traces is doing my favoruite combo- weaken gravity (spell that lets you jump higher) and then pushing someone. It'll push him much harder and higher, greatly raising a chance for instantly killing the enemy from the fall.