I too just went from $300 to $500 with them on my QS. but at the same time I was also approved for a Cabelas card ($500) with them.
I just tried for a CLI on my $1K Savor card after 3 months. They offered $100.
If you score goes up 50 points and you can not get the CLI you want, check prequals on Cap One page.
Often, you can get a much better limit and better APR and better rewards or terms by just opening a new account with Cap One.
Some backs require a HP just for CLI, Cap One does not.
Yes, Cap One with triple HP for a new account, but if you prequal for a Venture, you know you are going to get a good limit.
Cap One will grow with you as your credit gets better, you just have to take some inquiries like you would to open another account with another back (who might deny you or give you a lower CL)
My first opened card after starting rebuild was Cap One SL at $3k @ 25% apr.
My last opened card 4 years later was Cap One SL at $30k @ 14% apr.
DON'T WORK FOR CREDIT CARDS ... MAKE CREDIT CARDS WORK FOR YOU!
I always say something is better than a blank but this level is getting you nowhere and so it is in your best interest to focus on expanding your horizons and taking on new credit comparable with your stats with lenders who can help move your profile along a little more rapidly if that's what you expect. And they are out there. Just mill over those who grow nicely with their cardholders and some even give that boost you need right out of the gate.
As mention for 3 HPs UGH, you can gamble on a better new card with Capital One but the end choice comes down to what works best for you short and long term. Time doesn't wait, it goes on ahead and you can too.
Best of Luck on better satisfaction for your efforts.