This is exactly why it's sometimes difficult to push past your personal best times and improve, because when you do up the pace past your comfort level, things start to fall apart. I'll revisit the importance of having great visual skills which tend to be the key indicator of how well, fast and smooth you end up riding. You say that when you try and up your pace you end up making some small errors that compound over time and it sounds to me like turn entry speed is one area where things really get stressful.
What happens to your visuals when you try and enter a corner faster? Does your vision change? Does it narrow down or do you lose track of your wide vision? Can you still see all your Reference points?
For me, when I try and go fast, my vision gets behind a little and my perception of speed feels faster because of it. I get scared and then I over slow. Whatever gains I made in entering the corner faster, are therefore lost.
So, it starts with having great Reference Points, but then also has a ton to do with how and when I LOOK at those reference points. The key in almost all the situations is to NOT try and go fast but to work on improving your skills, one step at a time.
Quick story for you, you may have heard it before but here it is again. The first time I raced AMA 600 at Daytona I had never ridden the track before. I showed up a week before with the intent of spending the weekend club racing and learning the track before the AMA race but unfortunately on my second session around, I blew my motor on the banking. We scrambled to get a replacement motor sent from Oregon where my B Bike was (I couldn't afford to have both my bikes there) and that meant that I had just ONE Day to learn the track during the Team Hammer track day, before AMA qualifying the next day.
I went out for each practice session with a specific exercise to work on. First was Reference Points, in finding them and in drawing the track. I called Keith Code himself between sessions to talk through areas that I was struggling. Each session out I drew the track and added more RP's and before the final practice session of the day we compared may split times with everyone else's times (I was way off the pace) and chose the two corners where I was losing the most time.
Those two corners also happened to be the corners I had the fewest reference points in. For the last session I worked on finding more and better RP's and in putting my vision together so I flowed from one point to the other. The next day was qualifying and I didn't have much practice time to step up and find several seconds of improvement. I did the same thing, systematically working on putting my visuals together until the qualifying session came and Keith Code said "ok, you've done your work, now just RIDE, relax and have fun." I let go of everything and focussed on being smooth, relaxed and in having fun. I kept shouting in my helmet, "I'm riding DAYTONA!!!!" and sure enough when I came in, I had managed to find the time needed to qualify for the race!
So many times I caught myself trying to go FASTER instead of trying to improve and I had it all backwards. If you work on trying to improve your skills, how you roll on the gas, when you roll on, adding more RP's, remaining relaxed, not allowing your vision to narrow etc.....THAT is when you will find the speed.
You're on the right track. Keep up the hard work and you will find improvement in your times!!