Posting this because most relevant threads I've found are discussing automatic/small credit line increases. This pertains to larger increases and credit increase requests. My apologies if this has already been asked/answered elsewhere.
I have a Quicksilver and Venture X card, with a $2k and $20k credit line, respectively. I would like to request a credit line increase for my Venture card, since I mainly use that. I never use the Quicksilver card because the rewards aren't as good, so it just sits. I do keep it around in case I want to transfer my miles to dollars, which I do because, AFAIK, the conversion rate from miles to dollars with just the Venture card is about 80%.
Anyways, I'm hoping to increase my credit line for the Venture card to better help my credit score. So, what should I be requesting to likely get approved? I don't know if there is a cap, but from looking around this sub-reddit, the max line of credit I've seen is $40k. I don't know if I should ask them outright to double the credit line since that would be a big jump. However, I've never had a missed payment and have never accrued any interest.
For reference, my credit score is 807 and I only have these two credit cards. The free credit score report shows that the biggest improvement areas are my age of credit and my credit utilization (only 3%). I can of course wait for the score to go up as time goes on and my age of credit increases, but then the only other option is to increase my current lines of credit, or else open up a new card with Capitol One.
P.S., I have considered requesting an increase on the Quicksilver card, but I would bet that it has a better chance of being denied since I basically never use it. Any input on this route would be helpful as well.
EDIT: Clarification of details.