how often are those experience serveys? trying to get from 5/20 exp to level 2 so can try...

With being able to reset your skills now, if it doesn't decrease the amount of exp given per skill level (I.E. When you go up a skill level you get that level amount worth of EXP. If you go from 59 to 60 in smithing, you get 60 EXP towards your level up.
I'm not sure if going to Legendary skills cuts this, so that going from 59 to 60 will give only 30 EXP instead, for example.) then use skills you can use the most. If you're a sword and shield type, leveling heavy armor, one handed, block, will probably be
best for a speedy level up. Instead of being a sword and shield type, who's trying to use magic because its a skill set they don't usually use.

Something else to keep in mind is, as I explained with how getting EXP works, lower level skills, give you less EXP. If you never use Alteration Magic, sure you can make it go from 20 to 22 quickly, but you'll only get 21, and 22 EXP respectively. Where as
if you can make your smithing go from 59 to 60 in the same amount of time, you'll get 60 EXP instead.

So while leveling lower skills might seem like it'll make you level up faster, because you're raising the skills quicker, its actually not faster. Unless of course you can level quick enough to avoid losing EXP. If in the time it takes to go from 59 to 60 in
smithing, you can level Destruction from 20 to 25, then you'll get 115 EXP in the same amount of time it'll take you to get just 60 from smithing.

Again this is all based on that legendary skills don't give half the amount of EXP...Also, don't forget about skill books, and trainers! If you have the gold to spare, you can get a quick five levels in any of your skills. Choose the highest skill you have,
and go find a Master trainer. If you can level One-Handed from 90 to 95 with some gold and a few button presses, it'll give you a huge EXP jump on your next level.

I have a lvl 19 Infiltrator and to get to lvl 20 was around 500K exp, so that may be the last level.

From what I've seen so far, the first few levels are less than 1000EXP per level. Once you get to level 20 its about 10000EXP. After level 20, if you add 1100EXP to the previous level's EXP you are about right. i.e. Level 20 is 10000EXP, Level 11 is 11100EXP
(10000 + 1100 = 11100EXP) I'm level 31 and I need 22100EXP to rank to SR32.

"I am also going to focus on raising my really low skills like spell casting and pickpocket, try and bring some more balance to my levelling up. I still feel I may have handicapped my characters highest level."

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Think about it like this:

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Level 1 to level 2 = 2000 EXP.

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Skill from 15 to 16 = 650 EXP.

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Each given Skill increase gives a set EXP figure, not a percentage or anything variable like that. The total EXP gained from all Skills neither changes between races nor varies depending on when you level a given Skill up, so unlike in Oblivion, the maximum
level is certain. No handicapping done : )

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I'd be interested to see whether it's a clean levelup or you stop with progress to the next level.

About 10% of experience earned, whether you are at max level or not, is awarded as COD points. So during double exp weekend, you get double the money.