Apple's iMacs. Source: Apple. (via MacRumors) reported on Monday that refreshed versions of Apple's (NASDAQ: AAPL) 27-inch iMac and its 15-inch Retina MacBook Pro computers "will be available Wednesday." said the news comes from "well informed sources," but that it had "no further details."

Let's dig into this report a bit to see if this makes sense.

The MacBook Pro rumor checks out
As I wrote here, Intel (NASDAQ: INTC) -- supplier of Apple's Mac processors -- could have chips suitable for the Retina MacBook Pro ready to go by the end of the second quarter. In light of that, it would hardly be surprising to see Apple this week roll out a refreshed 15-inch Retina MacBook Pro based on Intel's quad-core mobile Broadwell processors.

What about the iMac rumor?
What I think requires a deeper dive is the rumor that Apple will refresh the 27-inch iMacs in a few days, with no mention of a refresh coming to the 21.5-inch iMacs.

First, let's review what kinds of processor and graphics configurations Apple offers for the 27-inch iMac.

According to AnandTech, Apple offers a "low-end" 27-inch iMac and a "high-end" model. The low-end model comes configured with a Core i5-4570 (3.2GHz base, 3.6GHz turbo) and an NVIDIA (NASDAQ: NVDA) GT 755M stand-alone graphics chip; Apple doesn't offer any built-to-order CPU/graphics upgrades for this model.

For the "high-end" model, the base configuration comes with a Core i5-4670 (3.4GHz base, 3.8GHz turbo) and an NVIDIA GTX 775M. Apple will allow customers to pay an extra $200 to boost the CPU to a Core i7-4771 (3.5GHz base, 3.9GHz turbo) and an additional $150 to move to an NVIDIA GTX 780M.

So far, so good. But here's where it gets tricky.

About these new Broadwell processors...
The two processors Intel is expected to release for desktops based on its Broadwell architecture are known as the i5-5675C and the i7-5775C. The i5-5675C is expected to feature four Broadwell cores at 3.1GHz base with turbo capability to 3.6GHz. The i7-5775C comes at 3.3GHz base with turbo capability to 3.7GHz.

Do you see the problem here yet? Let me explain.

The top Broadwell-based i7 that could go into a 27-inch iMac runs at a lower frequency than the top i7-4771 that customers can buy in the iMac today. Intel says Broadwell, per clock, is 5.5% faster than Haswell (the CPU inside all current iMacs) in a broad range of workloads. This means the top desktop Broadwell i7 should be roughly as fast as the top Haswell i7.

Now, if you want to be generous and assume the on-package eDRAM cache on the Broadwell parts will boost performance further, then the Broadwell chips could be a bit faster than the top Haswell parts in CPU workloads. However, it's not much of an upgrade.

Where the Broadwell chips should shine relative to the prior-generation Haswell chips is in situations in which the integrated graphics is used -- in other words, a low-end 21.5-inch iMac.

Here's what Apple could do
If Apple really is refreshing its 27-inch iMac models later this week, I could see the company moving the "low-end" 27-inch iMac from discrete graphics to integrated graphics. In particular, instead of offering just the Core i5 and the GT 755M, Apple might offer either a Core i5-5675C or a Core i7-5775C with no integrated option.

Then, I could see Apple more or less axing the current "high-end" model and bringing down the price points of the iMac with Retina 5K display. The iMac with Retina 5K display could then be upgraded to Intel's Skylake desktop processors, which are widely expected to arrive in the third quarter of 2015, later down the line, as well as updated discrete graphics chips.