Why is clone brush slowing and lagging?

Question

Before I explain my Lightroom issue, I want to describe my hardware platform because it may be relevant to solving my problem.
Asus P5B Deluxe motherboard
Intel Core 2 Duo E8400 3.0 mghz cpu
8 gigs Corsair ram
New Invidia EGVA GeForce 750 Ti with 2 gigs (video card)
Corsair 520 watt power supply
4 internal hard drives, all running at 7200 rpm
1 Samsung 250 gig SSD (sold state drive)
Windows 7 Home Premium 64bit, Svc pak 1
Lightroom 5.7
For the last several months I have been working with scanned 35mm slides. These, in some cases, are more than 60 years old. Time and dust have taken their toll and in doing so have provided me with many hours of Lightroom work. Typically, I am rebalancing color casts, exposures, tonal aberrations, noise induced by a careless scanning company, i.e. the usual types of edits one would perform in LR. Additionally, because of dust spots and emulsion abrasions on the slides, I am also making significant use of the Spot Healing Brush, which I use in the clone mode. This is a mighty fine and powerful tool which has allowed me to resurrect many a damaged image.
The scanned slides were returned to me as JPGs, which I have turned into TIF files to help them survive multiple edits and saves. The TIF files I am working with are mostly in the range of 40-45 mbytes.
Here’s my problem. About two weeks ago I began to notice that the more edits I performed on an individual file, the slower and more erratic the clone spotting brush became. This slowdown progressed from a near instantaneous selection and application of a clone patch to a crawling 3 to 4 seconds for the system to select a clone patch with up to 5 or 6 seconds for the patch to be applied to the defect area. Also, when I call the brush erratic, I mean that it jumps around somewhat not allowing me to position it accurately until the previous clone has been applied. Given the amount of work I still have to do on over 1000 slides, this is a state of affairs that is tough to tolerate.
Some of the slides have more than 60 or 70 edits showing in the History window. The vast majority of those edits on a given slide (I estimate 85% or more) represent individually cloned spots. The slowing typically begins at about 15-20 of these cloning edits and gets progressively worse as they accumulate.
So far I have taken the following steps to try to improve the situation. I have cleared the only LR caches I know about, those being the RAW cache and the video cache, neither of which would seem relevant given their names. I have deleted the History steps of images. I have moved my catalogs to the SSD drive. None of this has had a noticeable effect on the situation.
My question is: What’s going on here?
Are clone edits different from other edits in the way they are stored/written/cached?
Are edits typically written immediately to the catalog, or are they cached in ram or in the cpu cache?
What else could be happening to cause this behavior?
I am willing to upgrade my hardware. In fact I have ordered an Intel i7 cpu and appropriate motherboard and 16 gigs of ram. However, before I open these boxes I need more assurance that this upgrade will actually help the condition I am describing and that it is not some kind of hard limitation of Lightroom itself that will remain unrelieved by the upgrade.
I would welcome responses from anyone who could really explain what’s happening, particularly from Adobe staff. Thanks in advance for your help.
Bill Gordon

Answer 1

Here’s my problem. About two weeks ago I began to notice that the more edits I performed on an individual file, the slower and more erratic the clone spotting brush became.
This is a known issue with Lightroom. Lots of cloning or brushing will cause Lightroom to slow down.
There really isn't much to do about this. You could either:
Get a faster CPU, which should speed things up (whether or not it speeds up enough is unknown)
Do the cloning and brushing in Photoshop or Photoshop Elements, where there should be no speed issues in performing these tasks