Clot territory? Where'd you get that from?
My levels are much higher and they've been for a long time. No clots here. I even recently had an EEG and a Thallium stress test -- and I'm perfectly fine. My levels are above "normal" (normal is debatable) at around 2500 for the last three years (we don't know why). My cardo doctor said my levels are fine, and he didn't even blink when it came to smoking and HRT. And he's an expert on the circulatory system (endro's are not).
I had the cardio tests as a just in case test for something completely unrelated to HRT, being trans, etc. A Thallium stress test is where they put radio active die in you and you run on a tread mill, and then they take x-rays of your heart and arteries.
I wouldn't worry too much about your levels. If you're developing that's what matters most. If you develop symptoms of a clot, get it looked at, but taking estrogen doesn't mean you're gonna get a clot; nor is there an estrogen level that causes clots.
My pregnant friend's levels are around 9000. The normal range is between 250-ish-900-ish, but that's just a range, it will depends person to person. A lot of things can affect your estrogen... stress, the foods you eat, etc.
Also, more estrogen doesn't always = better or faster results. Actually, I just cut my dose (again) and my breasts have been growing like crazy.
Also, over time, you may notice sometimes that your estrogen levels will get slightly higher, that's fine and it happens. Sometimes you might have a bit of a dip in your levels, too, which is fine. Neither is a bad sign and it's not a huge health risk. Womens estrogen levels go up and down all of the time, by hundreds of units, every month.
So, don't sweat it. If you're developing, awesome. If you're not developing at all, talk to your doctor about a higher dose of estrogen and blockers. Most of all, enjoy becoming the woman you are and don't worry so much -- you're gonna be fine.

Good luck,
--natalie