There is quite a dense mini-cluster forming between Simcoe, Adelaide, Spadina and the rail tracks. By my count, there are eight towers taller than 100m built, under construction or proposed for that area:
208.4m 53f Ritz-Carlton Toronto (under construction)
198.9m 58f 300 Front Street West (proposed)
182.9m 42f RBC Centre (under construction)
156.7m 42f Bell Lightbox (under construction)
148.0m 33f Simcoe Place (built)
128.0m 27f Metro Hall West (built)
124.7m 34f M5V Life (proposed)
108.0m 36f Apex West (built)
Plus Apex East and the two Matrix buildings (already built), and the proposed 99 Blue Jays Way, all just under 100m (and 151 Front Street west, at 175.5m and 36f, half a block to the east of this area). Most of these are on the southern half of the area, but with a number of available parking lots and underutilised low-rise buildings on the northern half, so a few more talls could be built.
Bill
edit -- I took a screenshoot of the pdf image and measured the pixel count of the top portion using Paint, and compared the pixel count to the portions with heights given. The top portion is 15.01m by my measurement (probably exactly 15m), giving a total height of 198.9m = 653.6 feet.