Hello, I'm just a bit younger than hollywood (I'm 38), and have recently started taking a combined oral contraceptive as a form of hrt since I became menopausal (perimenopause started at age 32, my last period was about 10 months ago). My gynaecologist didn't see the point in waiting for a full year without periods because (i) I have a family history of early menopause (ii) I had a high FSH (iii) I had menopausal symptoms (complete dryness, hot flashes, insomnia.
The contraceptive I take is a new one called Qlaira. This is sometimes referred to as having bio-identical oestrogen (also called estradiol), but in fact it has a compound (oestrogen valerate) which is converted to oestrogen in the body. This oestrogen is chemically identical to that produced by the body.
Many hrt preparations use modified forms of estrogen to maximise its stability in the body (natural oestrogen is quickly broken down by the liver). "Equine oestrogen" from horse urine as used in Premarin/Prempro is in fact several slightly different oestrogen like compounds conjugated to side groups such as sulphate. The main one is converted to oestrogen in the body.
Evorel patches use a synthetic oestrogen which is chemically identical to natural oestrogen. It is present in the patch as "estradiol hemihydrate", which only refers to the present/absence of water molecules with the compound.
From my point of view, a "natural" oestrogen must come from a "natural" source, which isn't going to be human. This leads to the possibility, like with Prempro, that you may get other compounds present, and the effects of these may not be fully known. I would much rather have a synthetic form which is identical to human oestrogen ("bio-identical"?) such as Evorel, or which is converted to oestrogen (eg Qlaira) where the compound present is tightly controlled.
My gynaecologist prescribed Qlaira instead of hrt because it avoids the horse oestrogen problems, and has a dosing regime which avoids any mid-cyle bleeding. Since it contains a compound which is converted to oestrogen, and it contains progesterone, it is in essence the same as a oestrogen/progesterone hrt.
Sorry that's so long winded - I'm a biochemist and like talking about compounds ! 
Hollywood - hope it helped a little, and hope you find a happy solution soon.
Purplepeony - I think the "bio-identical" issue is definitely different to the dosage issue. On that point, I saw an interesting reference to the saliva test in Wikipedia, suggesting that it may not be so useful.
en.wikipedia.org/wiki/Hormone_replacement_therapy_(menopause)